1. Field of the Invention.
This invention relates to false-twisting apparatus and more particularly to friction rollers for driving high-speed twist tubes in false-twisting apparatus.
2. Description of the Prior Art.
False-twisting apparatus often uses friction rollers to twist a twist tube at speeds of up to 800,000 r.p.m. for example, by engaging the rollers against the twist tube. The friction rollers rotate at up to 40,000 r.p.m. and comprise a carrier of an inelastic material with a radial flange around the periphery of which a friction ring of an elastic synthetic resin material is secured. Such rollers are described in German Patent Specification No. 1,525,149. At least one of the rollers is driven. The twist tube is held in position against the rollers, by for example magnets.
A thread runs at a high speed through the twist tube. It passes around a twist pin in the tube either positioned at one end or at the midpoint of the tube. It is particularly advantageous to arrange the twist pin in the central region of the passage through the twist tube when the twist tube is to be rotated at extremely high speeds. In order to facilitate threading of the thread around the pin the tube has at least one transverse opening in the region of the pin.
In the false twisting process the thread to be false twisted runs over the surface of the twist pin under a certain amount of tension and is thereby squeezed so that the spinning oil that clings to the thread is removed or, where the thread is made up of a number of filaments, squeezed out of the thread. The oil is flung out through the transverse opening or openings in the twist tube as a result of the high centrifugal forces that are present, and it coats the adjacent parts of the associated false-twisting apparatus, in particular the regions of the friction rollers that face the twist tube pin.
This is a disadvantage insofar as the spinning oils, in particular the oils used im crimping, contain components which attack the friction rings of the rollers, which rings, because of the high loading, are made of a special material, for example polyurethane of predetermined hardness. The oil coating on the rings is particularly troublesome since it is important that the friction rings remain in a clean condition to promote smooth running of the twist tubes up to the highest possible speeds.
The coating of spinning oil causes the friction rings to lose their good running characteristics and to swell up and wear within a relatively short time. The idea of sucking away the mist or coating of spinning oil to avoid these problems is not practicable due to the lack of space and also because it is technically complicated and expensive.